1. Field of the Invention
The present invention relates to a chemical mechanical polishing (CMP) apparatus, and particularly to a pad feeding method suitable for use in a CMP apparatus.
2. Description of the Prior Art
Semiconductor fabrication has reached the deep sub-micron stage. In the deep sub-micron stage, the feature size and the depth of focus (DOF) of photolithography equipment are reduced, and the number of multi-level metal interconnect layers is increased. Consequently, how to maintain a high degree of surface planarity for the wafer has become a major topic of investigation.
Before the deep sub-micron era of semiconductor production, spin-on-glass (SOG) was employed to be the principle method of planarizing a silicon wafer. However, the method obtains moderate planarity in only local areas on the wafer surface. Without a global planarization of the wafer surface, quality of development after photographic exposure is degraded and the etching end-point is difficult to determine. These disadvantages reduce the yield of the wafer, and this reduction is a reason why SOG is substituted by chemical-mechanical polishing (CMP).
After semiconductor fabrication reached the deep sub-micron regime, CMP apparatus becomes a necessary apparatus of globally planarizing a silicon wafer. However, the polishing pad for a chemical mechanical polisher is a consumptive element. That is, the polishing pad needs to be changed after hundreds of polishing processes are performed.
FIG. 1 is a schematic view showing a conventional pad feeding mechanism in a CMP apparatus. As shown in FIG. 1, the CMP apparatus has a polishing platen 102 and a wafer carrier 110, wherein the wafer carrier 110 can hold a wafer 104 downward to the polishing platen 102. A polishing belt 100, serving as a plurality of polishing pads, is applied for use in the pad feeding mechanism. When a polishing pad (a portion of the polishing belt 100) on the polishing platen 102 needs to be changed, a terminal of the polishing belt 100 is pulled to spread out another unpolished portion of the polishing belt 100 to cover the polishing platen 102.
Other portions of the polishing belt 100 are rolled for space consideration. However, when the roller-type polishing belt 100 are wholly consumed, the CMP apparatus should have a shutdown for replenishing a new polishing belt. Such replenishment is complicated and time-consuming. There is therefore a need to improve this conventional pad feeding mechanism.